Method of electron beam exposure

DETAILED DESCRIPTION One object of this invention is to provide a method of electron beam exposure in which, when a resist film on a substrate is exposed with an electron beam, the scattering of the electron beam in the resist film and the backward beam scattering from the substrate can be suppressed by a simple operation to permit reduction of a proximity effect.
Another object of this invention is to provide a method of electron beam exposure in which, when a resist film on a substrate is exposed with an electron beam, the difference in the number-average molecular weight between the exposed area and the marginal area in the resist film is increased by a simple operation to permit the reduction of a proximity effect.
According to this invention, there is provided a method of forming a pattern on a resist film disposed on a substrate by exposing the portions of the resist film containing the pattern with an electron beam, the electron beam being directed onto the resist film a plurality of times at a fractional dose lower than a desired dose sufficient to produce a difference in molecular weight between the exposed area and the nonexposed area, the sum of the fractional doses corresponding to the desired dose.
Here, the desired dose means a dose determined so that, for the positive type resist film, the number average molecular weight (initial number average molecular weight) of the exposed area is less than two-thirds that of the nonexposed area and that, for the negative type resist film, the number average molecular weight (initial number average molecular weight) of the exposed area is two or more times greater than the nonexposed area.